Method and apparatus for the continuous production of cast or remelted billets using an electroslag method

ABSTRACT

The invention relates to a method and the apparatus required for carrying out the method for the continuous production of billets or ingots of metals, in particular steels and Ni- and Co-base alloys using the method of electroslag remelting or electroslag continuous casting in downwardly open water-cooled ingot molds ( 10 ), in which the billet ( 20 ) issuing downwardly from the ingot mold ( 10 ) is pressed against at least one guide element ( 24, 24, ) arranged rigidly in respect of its position with respect to the ingot mold axis (A), by at least one clamping element ( 26 ) arranged opposite the guide element, in such a way that the regions of the billet surface which are in contact with the guide or clamping elements ( 24, 26 ) change within short intervals of time, wherein at least one of said elements is driven to withdraw the billet while the others move with the billet and a contact with a current source can be made by way of at least one of said elements.

[0001] The invention concerns a method for the continuous production of billets or ingots of metal, in particular steels and Ni- and Co-base alloys using the method of electroslag remelting or electroslag casting in downwardly open water-cooled ingot molds and an apparatus which is suitable for same.

[0002] The continuous production of blooms or billets using the method of electroslag remelting or electroslag casting is basically known.

[0003] Thus for example Sh. Sasayama et al describe a method for the continuous remelting of self-consumable electrodes using the electroslag remelting method in a water-cooled ingot mold with continuous billet withdrawal by a draw-off apparatus.

[0004] Continuous production of remelted billets is made possible by use of the electrode change technology and cutting of the billets produced of small dimensions in the installation, in which respect the remelting rates for casting cross-sections of 130-250 mm² are specified at 180-275 kg/h and thus range in the area of 1.1-1.38 kg/h/mm billet thickness.

[0005] A. E. Vokov et al describe a continuous method for melting grinding dust in a slag bath heated by a non-consumable electrode in a water-cooled ingot mold with continuous billet withdrawal by a so-called bloom, clamping and draw-off apparatus. An autogenous cutting apparatus arranged in the installation permits the remelted billets produced to be cut to length. The remelting rates are specified at 210-240 kg/h for billets of a 300 mm diameter and are accordingly 0.7-0.8 kg/h/mm billet diameter.

[0006] AT 399 463 B discloses a method of electroslag continuous casting of steels and alloys, in which the casting surface in the water-cooled ingot mold is covered by an electrically conductive slag and in which the slag bath is heated for example when current passes therethrough by auxiliary electrodes which dip thereinto. In that method the casting speed is said to be so set that it is at least 1.5 times the melting-away rate which is usual in an electroslag remelting procedure and at most 50% of the casting speed in the case of conventional continuous casting. There is no information about the way in which the billet is withdrawn.

[0007] In addition U.S. Pat. No. 5,799,721 (corresponding to A 151/96) discloses a method of electroslag billet melting of metals, in which self-consumable electrodes whose cross-sectional area is 0.5 times the cross-sectional area of the remelting billet are remelted at a melting-away rate in kg/h, which corresponds to between 1.5 and 30 times the equivalent billet diameter calculated from the periphery of the casting cross-section, in accordance with D_(eq)=U/π in mm. There is also no information about the way in which the billet is drawn off.

[0008] On the other hand, very different arrangements are known for continuously drawing off the billets, for the continuous casting of steels and alloys, in which respect those apparatuses are always arranged at a considerable spacing from the water-cooled ingot mold and a secondary cooling section is generally disposed between the water-cooled ingot mold and the billet draw-off apparatus.

[0009] In the case of so-called arc installations the billet draw-off apparatus also has to perform the function of a continuously operating bending and straightening installation.

[0010] Draw-off apparatuses for continuously operating electroslag installations however must additionally also be in a position to carry away either all or at least a part of the melting current from the billet produced, without any interruption, in which respect consideration is to be paid to guiding the billet which is being drawn off, at a small spacing from the lower edge of the ingot mold.

[0011] Contact with a current source can basically be made with the clamping apparatuses referred to in the literature.

[0012] Both roller elements and also movable clamping jaw systems are known for the purposes of drawing off the billet. Roller elements enjoy the advantage that, when the billet is moving, the contact locations with the surface of the billet continuously change so that inadmissible cooling of the surface of the billet is avoided, even when using water-cooled rollers. On the other hand, taking off the melting current by way of rollers is admittedly possible by using brushes, but it is not entirely simple to implement that when higher current strengths are involved.

[0013] In contrast, in regard to taking off the current, clamping jaws with a relatively short stroke movement enjoy advantages as a fixed current-conducting connection is comparatively simple to make by using flexible line elements such as cables or bands. On the other hand clamping jaws which move with the billet in the draw-off movement thereof are in constant contact with the surface of the billet during the clamping phase so that, in a long clamping phase, unacceptable cooling of the surface of the billet can be caused at the contact locations. For that reason, the engagement times of clamping jaw elements may not be selected to be too long, in which respect it can be helpful, similarly as in the case of forging tools, to allow a certain rise in temperature of the clamping jaw contact surface.

[0014] In consideration of that state of the art the inventor set himself the aim of improving the known methods and apparatuses, avoiding the disadvantages noted, and dealing with the task, which is considerably different in comparison with continuous casting, of a continuous or stepwise withdrawal of the billet from the ingot mold in the electroslag remelting operation or electroslag continuous casting operation.

[0015] That object is attained by the teaching of the independent claim; the appendant claims set forth advantageous developments. The scope of the invention also embraces all combinations of at least two of the features disclosed in the description, the drawing and/or the claims.

[0016] In the method according to the invention, the billet issuing from the ingot mold is pressed against at least one guide element arranged rigidly in respect of its arrangement with respect to the ingot mold axis by at least one clamping element which is arranged in opposite relationship thereto in such a way that the contact points of the surface of the billet and the guide or clamping element continuously change, wherein at least one of those elements is driven for the purposes of drawing off the billet while the other moves with the movement of the billet and contact with a current source can be made at least by one of said elements.

[0017] In accordance with the invention, roller elements comprising one or more rollers are most suitable as the rigid guide element. It has proven to be desirable for the billet issuing from the ingot mold to be pressed against one or more rollers, the axes of which are arranged at 90° relative to the axis of the billet. In addition, the billet is to be drawn off by at least one roller against which the billet is pressed being driven.

[0018] The melting current is advantageously taken off by way of the clamping jaws which can be alternately pressed against the billet, in which respect the pressing times of the individual jaws do not exceed two minutes.

[0019] In order to keep short the contact times of the clamping jaws with the surface of the billet, the clamping jaws can preferably also be in the form of swing or rocking jaws which, similarly to a roller of large radius, roll along the surface of the billet during the clamping cycle.

[0020] The billet draw-off movement can be effected by one or more driven rollers or also by at least two clamping jaws of which one is always pressed against the billet and at the same time the draw-off movement is produced by a suitable device, while the second jaw is withdrawn and is returned to its upper position, in relation to the billet draw-off movement.

[0021] In that situation, the rollers which are not driven or the clamping jaws which are pressed against the billet also move with the draw-off movement of the billet, in which case the non-driven roller can be in the form of a measuring roller.

[0022] An apparatus suitable for carrying out the method according to the invention comprises a rigid frame which is aligned in relation to the axis of the ingot mold and which has at least two water-cooled guide rollers of which at least one is driven, and at least two clamping jaws which are connected to a current source and which can be pressed against the surface of the billet.

[0023] Further advantages, features and details of the invention will be apparent from the description hereinafter of a preferred embodiment and with reference to the drawing in which the single FIGURE is a diagrammatic view in longitudinal section through an apparatus according to the invention.

[0024] Disposed in a water-cooled ingot mold 10 which can also be in the form of a per se known funnel ingot mold is a slag bath 12 in which a self-consumable electrode 14 is being melted down. The melted-down metal is collected in a melting sump 16; the surface of the molten metal therein is identified by reference 18.

[0025] A billet 20 which is formed after setting is drawn off downwardly from the ingot mold 10 in the direction x by a driven roller 24 which is arranged in a rigid frame 22, in relation to the axis A of the ingot mold. Guidance for the billet 20 in parallel relationship to the axis A of the ingot mold is afforded by the above-mentioned driven roller 24 and further rollers 24 _(a), against which the billet 20 is pressed alternately by one of two clamping means 26 which are displaceable in a vertical direction.

[0026] A holding device 28 for the lower one of the two clamping means 26 carries an autogenous flame cutting device 30 with which the billet 20 produced can be cut to length in the phase of engagement of the clamping means 26. The clamping means 26 are connected to a current source 36 by way of flexible cables 32 and high-power lines 34.

[0027] In a particularly advantageous embodiment the jaws of the clamping means 26, which jaws are pressed alternately against the billet, are in the form of swing or rocking clamping jaws, the axes of which are arranged in the rigid frame 22 in such a way that the Clamping means 26 are movable in the billet draw-off direction x and their surface which is in contact with the billet 20 has a curvature with a radius corresponding to their axis spacing so that it rolls along the surface of the billet, in the condition of being pressed thereagainst.

[0028] As soon as the second swing clamping jaw is in engagement and therefore pressed against the billet, the jaw is retracted from the surface of the billet and the swing or rocking member is moved about the axis in opposite relationship to the billet draw-off direction into an upper starting position where it remains until the jaw is again pressed against the surface of the billet. 

1. A method for the continuous production of billets or ingots of metal, in particular steels and Ni- and Co-base alloys using the method of electroslag remelting or electroslag continuous casting in downwardly open water-cooled ingot molds, characterized in that the billet issuing downwardly from the ingot mold is pressed against at least one guide element arranged rigidly in respect of its position with respect to the axis of the billet by at least one clamping element arranged in opposite relationship thereto in such a way that the regions of the surface of the billet which are in contact with the guide and clamping elements change in short intervals of time, wherein at least one of the said elements is driven for the purposes of billet draw-off while the others move with the movement of the billet and contact with a current source is made by way of at least one of said elements.
 2. A method as set forth in claim 1 characterized in that the billet issuing from the ingot mold, for guidance of the billet, is pressed against one or more rollers whose axes are arranged at 90° relative to the axis of the billet.
 3. A method as set forth in claim 1 or claim 2 characterized in that the billet is drawn off by at least one driven roller against which the billet is pressed.
 4. A method as set forth in one of claims 1 through 3 characterized in that the billet is pressed against the guide element by two or more clamping jaws of which at least one is pressed alternately against the billet and moves with the draw-off movement of the billet while at least one is retracted from the surface of the billet and moved in opposite relationship to the billet draw-off direction into an upper end position and then pressed again against the surface of the billet and is moved with the billet before the at least one clamping means which is in engagement is retracted.
 5. A method as set forth in one of claims 1 through 4 characterized by a time of contact of a clamping means with the surface of the billet of at most two minutes.
 6. A method as set forth in at least one of claims 1 through 5 characterized in that current is taken off from the billet by way of the clamping jaws which are pressed against the billet and suitable lines to the connecting point of the current source.
 7. A method as set forth in one of claims 1 through 6 characterized in that an electrode change is effected for a fully continuous mode of operation.
 8. Apparatus for carrying out the method as set forth in at least one of claims 1 through 7 characterized by at least two guide elements (24, 24 _(a)) which are arranged parallel to the axis (A) of the ingot mold in a frame (22) but which are movable in the direction of the axis and at least one clamping element (26) which is arranged in opposite relationship thereto and which can be pressed in the direction of the guide elements and which permits a movement in the direction of the axis of the ingot mold both in the condition of being pressed against the billet and also in the released condition, and that one of said elements is driven and a connection to a current source (36) can also be made by one of said elements.
 9. Apparatus as set forth in claim 8 characterized in that the guide elements are in the form of rollers (24, 24 _(a)).
 10. Apparatus as set forth in claim 8 characterized in that displaceable jaws are provided as elements in the direction of the axis (A) of the billet.
 11. Apparatus as set forth in claim 8 characterized in that the elements are in the form of swing jaws whose contact surface with the surface of the billet has a curvature whose radius corresponds to the spacing from the swing axis. 